When a thin film on a semiconductor wafer is etched by plasma, it is necessary to correctly detect an end point of the etching to prevent a shortage of etching and overetching. The end point of the etching is able to be determined by observing a change of emission intensity of plasma by using a spectroscope.
For example, when a patterning is performed for an insulating film formed on an etching stopper film by the etching, the etching stopper film at a lower layer is exposed when the insulating film is removed by the etching. At this time, plasma with a wavelength resulting from the etching stopper film begins to be generated in an etching apparatus. Accordingly, it is possible to judge the end point of the etching of the insulating film from a change of the emission intensity of the wavelength if an emission wavelength of the plasma generated at the etching time of the etching stopper film is examined in advance.
Here, there is a case when light-emission of plasma with plural wavelengths is measured to correctly detect the etching end point. The emission wavelengths of the plasma to be measured are determined in accordance with the following processes. At first, the emission intensities of the plasma with plural wavelengths are obtained by performing the etching processes for one time or more. Subsequently, waveforms of the emission intensities of the plural wavelengths are cluster analyzed, and plural groups are classified based on resemblance of waveforms. Further, a representative wavelength is selected from each group. The end point of the etching is determined by examining changes of the emission intensities of the representative wavelengths selected as stated above.    [Patent Document 1] Japanese Laid-open Patent Publication No. 2004-235361    [Patent Document 2] Japanese Laid-open Patent Publication No. 2010-219263
However, when the end point is judged by the emission intensity of the plasma emission wavelength resulting from the insulating film and the etching stopper film, there is a possibility in which the overetching and the shortage of etching occur because the end point is judged after the change of the emission intensity is observed.
Besides, it becomes impossible to correctly detect a variation of the emission intensity of the plasma and therefore to correctly detect the etching end point when a part of data lacks, or noises mix into the data from external. Further, it is impossible to correctly detect the variation of the emission intensity of the plasma, and to correctly detect the end point of the etching when a value of a part of data changes discontinuously.